1. Field of the Invention
The present invention relates to a vibrating gyroscope, and more particularly to a vibrating gyroscope for measuring the rotational angular velocity for use in techniques such as navigation of cars, control of vehicle attitude, and correction of camera shake.
2. Description of the Related Art
FIG. 14 is a perspective view illustrating an example of a conventional vibrator, and FIG. 15 is a block diagram showing a conventional vibrating gyroscope having the vibrator. A vibrator 1 comprises a vibrating body 2 in a form such as a regular triangular prism. Piezoelectric devices 3a, 3b, and 3c are formed in the center portions of the three side-surfaces of the vibrating body 2, respectively. The piezoelectric devices 3a and 3b are connected to electric charge detecting circuits 4a and 4b, and output signals of the electric charge detecting circuits 4a and 4b are added and then input into driving circuit 5. In the driving circuit 5, the input signal is amplified and phase-corrected, and the obtained signal is in turn supplied to the piezoelectric device 3c as a driving signal. This results in a bending vibration of the vibrating body 2 in the direction perpendicular to the surface on which the piezoelectric device 3c is formed.
The electric charge detecting circuits 4a and 4b are also connected to a detecting circuit 6. The detecting circuit 6 comprises a differential circuit, a synchronous detection circuit, a smoothing circuit, and a DC amplifier circuit, etc. In the differential circuit, the difference between the output-signals of the electric charge detecting circuits 4a and 4b is obtained and the output-signal of the differential circuit is in turn detected, smoothed, and amplified. When there is no rotation, since the states of bending of the piezoelectric devices 3a and 3b are the same, electric charges generated in the piezoelectric devices 3a and 3b are the same. Therefore, output signals from the electric charge detecting circuits 4a and 4b are the same, and an output signal of the detecting circuit 6, where the difference of the output signals therebetween is measured, is zero. When the vibrating body 2 is rotated about its axis at an angular velocity .omega., as shown in FIG. 14, the direction of the bending vibration in the vibrating body 2 is changed by means of a Coriolis force. Accordingly, the bending states of the piezoelectric devices 3a and 3b are changed to generate a difference in the charges generated by the piezoelectric devices 3a and 3b, and to generate a difference in the output signals from the electric charge detecting circuits 4a and 4b. Therefore, a signal is output from the differential circuit of the detecting circuit 6 and the signal in turn is detected, smoothed, and amplified to obtain a DC signal corresponding to the angular velocity.
There is also known a vibrating gyroscope which comprises a vibrator utilizing a tuning fork-shaped vibrating body 2, as shown in FIGS. 16 and 17. In this vibrator 8, the vibrating body 2 is formed by driving plates 2a and detecting plates 2b, with surfaces thereof being disposed perpendicular to each other. In the driving plates 2a, piezoelectric devices for driving 7a are formed while in the driving plates 2b, piezoelectric devices for detecting 7b are formed. Between the two piezoelectric devices for driving, a driving circuit is connected and an output signal from one piezoelectric device 7a for driving is used as feedback to supply a driving signal to another piezoelectric device 7a for driving. This results in vibrating the vibrating body 2 so as to open/close it.
When there is no rotation, since the detecting plates 2b move in the directions of their widths, no bending is generated in the detecting plates 2b. Accordingly, the output signal becomes zero, which indicates no rotational angular velocity. When a rotational angular velocity is generated about the axis of the vibrating body 2, a bending vibration is generated by means of a Coriolis force in the direction perpendicular to the surfaces of the detecting plates 2b, i.e. in the direction of the thickness of the detecting plates 2b. At this time, as two detecting plates bend in the directions opposite to each other, a difference is generated in the charges generated by the two piezoelectric devices 7b which can be converted to a DC signal corresponding to the Coriolis force.
In these vibrating gyroscopes, the output sensitivity may be varied depending on changes in the outside environment, vibrations, physical shocks, etc. These vibrating gyroscopes, however, have no way of diagnosing changes in an output sensitivity by themselves and have not been able to judge their failures.